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RESEARCH ARTICLE
Incidence of splenic malignancy and
hemangiosarcoma in dogs undergoing
splenectomy surgery at a surgical specialty
clinic: 182 cases (2017–2021)
Brigita Ziogaite
1
*, Elena T. ContrerasID
2
, Jason E. Horgan
1
1Leader Animal Specialty Hospital, Cooper City, Florida, United States of America, 2Shreiber School of
Veterinary Medicine of Rowan University, Mullica Hill, New Jersey, United States of America
*briggitaz@yahoo.com
Abstract
The objectives of this study were to evaluate the risk and predictive factors of splenic malig-
nancy and hemangiosarcoma in dogs undergoing splenectomy at a surgical specialty clinic.
Medical records, hematologic results, surgical reports, and histopathologic results from 182
dogs that underwent splenectomy for the treatment of splenic masses or nodules were
reviewed retrospectively. The majority of dogs (57.7%) had benign splenic diagnoses with
no malignancy. Hemangiosarcoma was diagnosed in 32.4% of the dogs. A final multivari-
able model indicated that thrombocytopenia, anemia, and a smaller diameter of the largest
splenic nodule were risk factors for hemangiosarcoma (P<0.001), and hemoperitoneum (P
= 0.01) was an additional risk factor when nodule diameter was not evaluated. There were
91 dogs that had hemoperitoneum, and 60.4% of those dogs had malignant splenic lesions.
Of the 33 dogs that underwent a splenectomy for incidentally identified splenic lesions,
93.9% had benign splenic lesions. Breed size was not a significant predictor of splenic
malignancy risk; however, all 6 of the German shepherds included in the study had a
hemangiosarcoma diagnosis. Overall prevalence of splenic malignancy including HSA may
be overestimated in some canine populations.
Introduction
Canine splenic masses are commonly encountered in veterinary practice. Size and distribution
of the masses range from small focal or multifocal nodules to large cavitated masses, and they
originate from a variety of tissues including lymphoid, vascular, fibrous, smooth muscle, and
endothelial tissues. Benign splenic masses are usually diagnosed as hemangiomas, hematomas,
or lymphoid hyperplasia [1–3], while the most commonly reported malignant tumor of the
spleen is hemangiosarcoma (HSA) [2–6]. Based on appearance and clinical presentation, HSA
and other malignant splenic lesions can be indistinguishable from benign splenic lesions; how-
ever, it is important to predict the likelihood of HSA or malignancy due to the poor prognosis
associated with these diagnoses.
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OPEN ACCESS
Citation: Ziogaite B, Contreras ET, Horgan JE
(2024) Incidence of splenic malignancy and
hemangiosarcoma in dogs undergoing
splenectomy surgery at a surgical specialty clinic:
182 cases (2017–2021). PLoS ONE 19(12):
e0314737. https://doi.org/10.1371/journal.
pone.0314737
Editor: Sudheesh Sreerangam Nair, Ross
University School of Veterinary Medicine, SAINT
KITTS AND NEVIS
Received: May 3, 2024
Accepted: November 14, 2024
Published: December 3, 2024
Copyright: ©2024 Ziogaite et al. This is an open
access article distributed under the terms of the
Creative Commons Attribution License, which
permits unrestricted use, distribution, and
reproduction in any medium, provided the original
author and source are credited.
Data Availability Statement: All relevant data are
within the paper. Due to client confidentiality of
medical records, surgical reports and
histopathology reports cannot be shared publicly.
Any relevant data that can be shared without
compromising client confidentiality is shared on
figshare: https://figshare.com/s/
83ce609b5ee0494b5d6c or DOI 10.6084/m9.
figshare.26352820.
To better understand the likelihood of splenic malignancy, studies have explored numerous
factors associated with benign and malignant splenic masses [7–9]. Factors such as breed, gen-
der, neuter status, age, body size, hematologic values, mass-to-splenic volume ratio, spleen-to-
body-weight percentage, and number of lesions present on the spleen have been investigated
with variable results [7,10–12]. Presence of hemoperitoneum, anemia, thrombocytopenia,
macroangiopathic hemolysis with presence of schistocytes, disseminated intravascular coagu-
lation, and low total solids concentration have all been reported as associated with HSA [12–
14].
One of the most common considerations when making clinical decisions regarding the
likelihood of splenic malignancy and HSA when a splenic lesion is found, is the “double two-
thirds” rule that states that approximately two thirds of splenic masses in dogs with spleno-
megaly are malignant, and two thirds of those are diagnosed as HSA [13]. This rule is often
applied to all splenic masses with and without hemoperitoneum and is strongly established in
clinical settings. Some recent studies [7,8,15] have not aligned with these early findings; never-
theless, splenectomy is typically performed as a treatment for patients with a splenic mass,
although in most cases, it is performed without knowing if the mass is benign or malignant.
Guidelines regarding prognostic indicators for splenic malignancy and HSA warrant fur-
ther investigation in different populations in different time periods. Preoperative diagnostics
are continually advancing, canine demographics and breed distributions might be changing,
and the histopathological findings of splenic masses and clinical patterns may differ from
those established decades ago. Furthermore, patient and client populations might differ in
non-university settings, and such critical decisions and guidelines must be based on risk suited
to the setting. For instance, the economic burden of splenectomy surgery combined with a
poor prognosis for an HSA diagnosis, can result in the unnecessary euthanasia of patients with
benign splenic masses, especially in emergency settings where owners must make rapid deci-
sions [16]. Splenectomy for benign masses can also result in shortened lifespans, as periopera-
tive complications can arise and result in death [17–19]. Thorough knowledge of splenic
pathology, risk factors for malignancies, and continuous reevaluation of data are needed to aid
in the decision-making process for both clinicians and owners.
The objective of this study was to update the literature regarding the likelihood of malig-
nant splenic neoplasia and HSA in dogs undergoing splenectomy after splenic nodules or mas-
ses were identified at a surgical specialty clinic. Our secondary objective was to identify factors
predictive of HSA in this population of dogs. We hypothesized that, of the dogs undergoing
splenectomy due to splenic lesions diagnosed at a specialty surgical practice, less than 66.7% of
the splenic lesions would be histologically identified as neoplastic, and less than 44% would be
histologically identified as HSA.
Methods
Case identification
An electronic medical records search was performed to identify dogs that underwent splenec-
tomy surgery at Leader Animal Specialty Hospital between September 2017 to July 2021. Dogs
with or without hemoperitoneum were included in the study if they had singular or multiple
splenic masses or nodules and had a splenectomy performed as treatment for the splenic
lesions. All surgeries were performed by board certified veterinary surgeons (ACVS diplo-
mates), a residency trained surgeon, or surgical residents. A splenectomy surgical report and a
complete histopathology report for the splenic nodule(s) or mass(es) tissues excised during
splenectomy were required for inclusion. Dogs were excluded if they had a history of traumatic
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Canine splenectomy, splenic malignancy, and hemangiosarcoma at a surgicalspecialty clinic
PLOS ONE | https://doi.org/10.1371/journal.pone.0314737 December 3, 2024 2 / 15
Funding: The author(s) received no specific
funding for this work.
Competing interests: The authors have declared
that no competing interests exist. Two of the
authors [BZ and JH] are employed by Leader
Animal Specialty Hospital. This does not alter our
adherence to PLOS ONE policies on sharing data
and materials.
splenic rupture, immune mediated thrombocytopenia (IMTP), splenic torsion, splenic absces-
sation, or gastric dilatation-volvulus (GDV) leading to splenic vascular disruption.
Data collection
Data collected from the medical records included dog’s age at splenectomy, breed, sex, neuter
status, body weight, hematocrit (HCT), platelet count (PLT), other diagnostics, presence of
nontraumatic hemoperitoneum, presence of pulmonary metastasis, perioperative anesthetics,
documented reason for splenectomy, number and diameter of splenic nodules or masses,
splenic histologic diagnosis, and successful survival to discharge.
Breeds were self-reported by the owner and recorded in the medical record. Breeds that
were represented by more than five dogs were analyzed as individual breeds within a breed-
size category. All other breeds, including dogs reported as mixed-breed dogs, were grouped by
size into five additional categories: toy (1.0–4.9 kg), small (5.0–9.9 kg), medium (10.0–17.9 kg),
large (18.0–35.9 kg), and extra-large (36.0 kg and higher). Therefore, a breed-size category was
created that included breeds represented by more than 5 dogs and the 5 size categories.
HCT and PLT were obtained from the complete blood count (CBC) preoperative labora-
tory values. If a preoperative CBC was not available in the records, packed cell volume (PCV)
on the day of surgery was substituted for the HCT. Both HCT and PLT were classified into cat-
egories based on the reference intervals at the surgical specialty clinic. HCT was classified into
three categories: low (<33%), normal (33%–56%), and high (>56%). Platelet count was clas-
sified into 5 categories: very low (0 – 59K/uL), low (60–117), low normal (118–249), normal
(250–490), and high (>490).
Histopathologic splenic diagnoses were retrieved from veterinary pathologists’ (ACVP dip-
lomates) histopathology reports from the veterinary diagnostic laboratories where the splenic
tissues were submitted post-operatively. Diagnoses were categorized as hemangiosarcoma
(HSA), splenic malignancy including HSA, splenic malignancy other than HSA, and benign
with no splenic malignancy. The presence of nontraumatic hemoperitoneum was confirmed
with medical record documentation of peritoneal blood at or near the time of splenectomy.
The number and diameter of splenic nodules or masses were collected from surgery reports. If
multiple measurements from multiple lesions were identified, the diameter of the largest nod-
ule or mass was used. Splenectomies performed due to incidental findings of splenic abnor-
malities intraoperatively during an unrelated surgery, were recorded and categorized as non-
primary surgeries, while splenectomies performed during a scheduled splenectomy surgery
were categorized as primary surgeries. Pulmonary metastatic disease diagnosis was based on
the presence or absence of pulmonary nodule(s) on preoperative thoracic radiographic or
computerized tomography (CT) imaging and recorded based on the veterinary radiologists’
(ACVR diplomates) reports when available. A dog was considered to be discharged success-
fully if the dog was released with standard post-operative recovery instructions. A dog was
considered to be discharged unsuccessfully if the dog was euthanized or died after surgery but
prior to discharge, or if the dog was released to the owner at the owner’s request to be eutha-
nized at home or at another clinic.
Statistical analysis
Data were described and analyzed using STATA version 14.2 (StataCorp. 2015. College Sta-
tion, TX, USA). Descriptive statistics were calculated, and categorical data were expressed as
frequencies and percentages, whereas continuous data were expressed as medians and ranges.
The Shapiro-Wilk test was used to assess normalcy of continuous data (PLT and HCT);
because of non-normalcy, the Wilcoxon rank sum test was used to compare median PLT and
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HCT in dogs diagnosed with HSA compared to median PLT and HCT in dogs with a benign
diagnosis. Logistic regression modeling was used to assess the association between variables
(age, sex, breed-size group, primary surgery, PLT, HCT, presence of hemoperitoneum, tho-
racic metastasis, number of splenic nodules, diameter (cm) of largest splenic nodule or mass)
and diagnosis of malignancy and diagnosis of HSA. Variables with a liberal significance
threshold of P<0.20 in univariable analyses were considered for inclusion in the final multi-
variable model. The Hosmer-Lemeshow statistic was used to test the overall fit of the model.
The area under the ROC curve was used to evaluate the discriminatory ability of the model to
predict HSA. Statistical significance was set at P<0.05.
Ethics statement
This manuscript was retrospective in nature and utilized data from clinical patients. All data
was anonymized prior to use. Given the retrospective nature of this manuscript, prospective
approval from the Institutional Animal Care and Use Committee (IACUC) was not required,
as it was deemed not necessary by a university IACUC.
Results
Initial record screening resulted in the identification of 206 dogs that underwent splenectomy
during the study period. Of these dogs, 182 dogs met the criteria for study inclusion. The
median age of dogs was 11 years (range 3 to 17 years). There were 84 females, 4 of which were
intact, and there were 98 males, 9 of which were intact. The median body weight was 22.2 kg
(range 1.2 to 53.2 kg). There were 54 breeds reported by owners. Mixed-breed dogs were most
commonly reported (41/182, 22.5%), and these 41 dogs were reassigned to the size categories
within the breed-size category. There were 5 breeds that consisted of more than 5 dogs
(Table 1).
Benign diagnoses with no malignancy were made in a total of 105 dogs (57.7%), while diag-
noses of splenic malignancy including HSA were made in a total of 77 dogs (42.3%). HSA was
diagnosed in 59 dogs (32.4%). A splenic malignancy other than HSA occurred in 21 dogs
(11.5%); 2 of these dogs had a concurrent diagnosis of both HSA and lymphoma, and 1 of
these dogs had a diagnosis of HSA or histiocytic sarcoma. Splenic malignancies other than
HSA included liposarcoma (n = 2), lymphoma (n = 6), carcinoma (n = 1), splenic sarcoma
(n = 8), and plasma cell tumor (n = 1) (Table 2).
Table 1. Breed-size category and hemangiosarcoma diagnosis.
Breed-size category Number (%) of dogs Number (% of breed-size category) of dogs with HSA
Labrador retriever 15 (8.2%) 8 (53.3%)
Boxer 12 (6.6%) 5 (41.7%)
Bull terrier 10 (5.5%) 2 (20.0%)
German shepherd 6 (3.3%) 6 (100%)
Golden retriever 6 (3.3%) 4 (66.7%)
Extra-large (�36.0 kg) 12 (6.6%) 3 (25.0%)
Large (18.0–35.9 kg) 36 (19.8%) 6 (16.7%)
Medium (10.0–17.9 kg) 37 (20.3%) 13 (35.1%)
Small (5.0–9.9 kg) 32 (17.6%) 8 (25.0%)
Toy (1.0–4.9 kg) 16 (8.8%) 4 (25.0%)
TOTAL 180 59 (32.8%)
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Hemoperitoneum was present in 91 (50%) dogs. Of these 91 dogs, 55 (60.4%) had a splenic
malignancy including HSA, while 36 of the dogs (39.6%) with hemoperitoneum had no malig-
nancy. Of the 91 dogs with hemoperitoneum, 44 had HSA (Table 2).
The number of splenic masses or nodules was recorded for 180 (98.9%) of the dogs. The
180 dogs had one (n = 131), two (n = 13), three (n = 2) or multiple (n = 34) nodules. The 2
dogs with three nodules were reclassified as having multiple nodules. Diameter of the largest
nodule was recorded for 143 dogs (78.6%); median diameter was 9.2 cm (range 0.5 cm to 40
cm).
Thirty-three of the dogs (18%) had a splenectomy performed as a non-primary surgery due
to an incidental finding of a splenic nodule or mass during another surgery. Of these 33 dogs,
31 (93.9%) did not have a splenic malignancy. Only 2 (6.0%) of the 33 dogs had an HSA. None
of the dogs that had a splenectomy due to incidental findings during surgery, had a non-HSA
splenic malignancy (Table 2).
There was no evidence of thoracic metastasis in 172 (95%) of the dogs. Evidence of thoracic
metastasis was only found in 3 dogs (2%), and they had splenic diagnoses of HSA, lymphoma,
and hematoma. For the dog with a diagnosis of splenic hematoma, the CT report stated that
pulmonary nodules were suspected to represent metastatic neoplasia, though osseous metapla-
sia was another differential. Thoracic radiograph interpretation was inconclusive for 6 dogs,
and neither radiographs nor a report was located in the medical record for 1 dog. A veterinary
radiologist (ACVR diplomate) report was located in the medical records for 176 (97.2%) of the
dogs; for 5 of the dogs, image interpretation was performed by one of the surgeons.
There were 166 (91%) dogs that survived to discharge. Of the 16 dogs (8.8%) that were not
successfully discharged, 7 had an HSA diagnosis, 1 had a carcinoma, and 8 had no malignancy
diagnosed (Table 2). There were 10 additional dogs that were euthanized or died intraopera-
tively or immediately postoperatively; however, these 10 dogs were not included in the 182
dogs of this study cohort and analyses, as the owners did not consent to splenic
histopathology.
The median HCT was 36% (range 10.8%–72.4%). There were 2 dogs for which full blood-
work was not reported in the records. For those 2 dogs, PCV on the day of surgery was used in
analyses. A low HCT was reported in 66 dogs (36.3%), while 110 dogs (60.4%) had a normal
HCT, and 6 dogs (3.3%) had a high HCT. No dogs with a high HCT had a splenic malignancy.
HCT values of dogs with a diagnosis of HSA (n = 59, median 29.6%, range 15.2% to 49.9%)
were significantly lower (P<0.001) when compared to HCT values of dogs with a benign diag-
nosis and no malignancy (n = 105, median 39.3%, range 10.8% to 72.4% (Fig 1).
Table 2. Histologic diagnoses of 182 dogs that underwent splenectomy.
Diagnosis Number (%) of
dogs
Number (%) of dogs with
hemoperitoneum
Number (%) of dogs with non-primary
splenectomy
Number (%) of dogs not surviving
to discharge
Hemangiosarcoma
1
59 (32.4%) 44 (24.2%) 2 (1.1%) 7 (3.8%)
Other malignancy not
HSA
18 (9.9%) 11 (6.0%) 0 (0.0%) 1 (0.5%)
Other malignancy and
HSA
1
3 (1.6%) 2 (1.1%) 0 (0.0%) 0 (0.0%)
Benign and no
malignancy
105 (57.7%) 36 (19.8%) 31 (17.0%) 8 (4.4%)
TOTAL 182 (100%) 91 (50%) 33 (18.1%) 16 (8.8%)
1
The one dog with a diagnosis of HSA or histiocytic sarcoma is included in this category.
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The median PLT was 156K/uL (range 17 – 932K/uL) (Table 3). Of the 55 dogs with normal
or high PLT, only 4 had HSA. PLT counts of dogs with a diagnosis of HSA (n = 59, median
105, range 17 to 59K/uL) were significantly lower (P<0.001) when compared to PLT counts of
dogs with a benign diagnosis and no malignancy (n = 103, median 215, range 21 to 932K/uL)
(Fig 2).
Fig 1. Boxplot comparison of hematocrit (HCT) percentages in dogs with and without hemangiosarcoma (HSA). Boxplot illustrates the
distribution of HCT percentages among dogs diagnosed with hemangiosarcoma (n = 59) as compared to dogs with a benign splenic diagnosis
and no malignancy (n = 105). The median and interquartile ranges are represented by horizontal lines and shaded boxes, respectively. Whiskers
extend to the 5
th
and 95
th
percentiles. Dogs with HSA showed significantly lower HCT percentages as compared to dogs with a benign splenic
diagnosis and no malignancy. (Wilcoxon rank sum test, P<0.001).
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Table 3. Platelet counts and splenic malignancy.
Platelet count
category
Number (%) of
dogs
Number (%) of dogs with
HSA
Number (%) of dogs with NO splenic
malignancy
Very low (0-59K/uL) 30 (16.7%) 14 (7.8%) 13 (7.2%)
Low (60-117K/uL) 38 (21.1%) 22 (12.2%) 13 (7.2%)
Low normal (118-
249K/uL)
57 (31.7%) 19 (10.6%) 34 (18.9%)
Normal (250-490K/uL) 44 (24.4%) 3 (1.7%) 34 (18.9%)
High (>490K/uL) 11 (6.1%) 1 (0.5%) 9 (5.0%)
TOTAL 180 59 (32.8%) 103 (57.2%)
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Univariable logistic regression modeling identified six variables with liberally significant
(P<0.20) association with HSA diagnosis: breed-size (P = 0.12, Table 1), PLT, HCT, primary
surgery, presence of hemoperitoneum, and diameter (cm) of largest splenic nodule or mass.
These variables were further evaluated using multivariable regression modeling. The final mul-
tivariable model for risk of HSA retained three significant risk factors, PLT, HCT, and diame-
ter of largest splenic nodule or mass (Table 4). The final model fit the data well based on the
Hosmer-Lemeshow statistics (χ
2
= 8.23, P = 0.41) and showed good discrimination (area
under the ROC curve = 0.81). Controlling for other variables in the model, the odds of HSA
diagnosis were, on average, 21.4 times higher (95% CI 3.97 to 115.27, P<0.001) in dogs with
low PLT (60K-117K u/L) as compared to dogs with normal PLT. The odds of HSA diagnosis
were, on average, 3 times higher (95% CI to 1.27 to 7.51, P = 0.01) in dogs with a low HCT
(<33%) as compared to dogs with a normal HCT. No dogs with a high HCT had HSA. For
each 1 cm increase in the diameter of the largest splenic nodule, the odds of HSA diagnosis
decreased, on average, by 10% (OR = 0.90, 95% CI 0.84 to 0.97, P = 0.01).
Because some dogs (n = 39) did not have splenic nodule diameters recorded in their rec-
ords, logistic regression modeling was also performed excluding diameter as a variable. The
Fig 2. Boxplot comparison of platelet count (PLT) in dogs with and without hemangiosarcoma (HSA). Boxplot illustrates the distribution of
PLT (K/UL) among dogs diagnosed with hemangiosarcoma (n = 59) as compared to dogs with a benign splenic diagnosis and no malignancy
(n = 105). The median and interquartile ranges are represented by horizontal lines and shaded boxes, respectively. Whiskers extend to the 5
th
and 95
th
percentiles. Dogs with HSA showed significantly lower PLT percentages as compared to dogs with a benign splenic diagnosis and no
malignancy. (Wilcoxon rank sum test, P<0.001).
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final multivariable model for risk of HSA retained three significant risk factors, PLT, HCT,
and hemoperitoneum (Table 5). The final model fit the data well based on the Hosmer-Leme-
show statistics (χ
2
= 6.81, P = 0.45) and showed good discrimination based on performance
under the ROC curve (AUC = 0.79). Controlling for other variables in the model, the odds of
HSA diagnosis were, on average, 2.9 times higher (95% CI 1.28 to 6.37, P = 0.01) in dogs with
hemoperitoneum as compared to dogs without hemoperitoneum.
The following variables were not associated with HSA diagnosis: sex (P = 0.38), number of
splenic nodules (P = 0.86), thoracic metastasis (P = 0.99), and age (P = 0.64).
When evaluating all splenic malignancy diagnoses including HSA in a multivariable model,
logistic regression modeling identified five variables for inclusion in the model: PLT, HCT,
primary surgery, presence of hemoperitoneum, and diameter (cm) of largest splenic nodule or
mass (Table 6). The final model fit the data well based on the Hosmer-Lemeshow statistics (χ
2
= 8.55, P = 0.38) and showed good discrimination (area under the ROC curve = 0.81).
Discussion
This study documented the histopathologic distribution of canine splenic masses treated by
splenectomy at a privately owned specialty practice. In the present study, HSA was identified
Table 4. Summary of multivariable analysis and hemangiosarcoma diagnosis.
Categorical variable Level Number P-value Coefficient Odds ratio (OR) OR 95% Confidence Interval
Platelet group*Very low (0-59K u/L) 30 0.1 4.49 4.43 0.75 to 26.08
Low (60K-117K u/L) 38 <0.001 3.06 21.4 3.97 to 115.27
Low normal (118K–249K u/L) 57 0.01 2.12 8.35 1.65 to 42.38
Normal (250K-490K u/L) 44 reference reference reference reference
High (>490K u/L) 11 0.21 1.76 5.83 0.38 to 89.88
Hematocrit*Low (<33%) 66 0.01 1.13 3.09 1.27 to 7.51
Normal (33%–56%) 110 reference reference reference reference
High (>56%) 6 perfect predictor of no hemangiosarcoma
Diameter of largest nodule*centimeters 143 0.01 -0.1 0.9 0.84 to 0.97
Hemoperitoneum No 91 reference reference reference reference
Yes 91 0.06 0.92 2.52 0.97 to 6.55
*significant P-value at P<0.05.
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Table 5. Summary of multivariable analysis and hemangiosarcoma diagnosis (without diameter included).
Categorical variable Level Number P-value Coefficient Odds ratio OR 95% Confidence Interval
Platelet group*Very low (0-59K u/L) 30 0.02 1.69 5.43 1.28 to 23.05
Low (60K-117K u/L) 38 <0.001 2.5 12.13 3.03 to 48.54
Low normal (118K–249K u/L) 57 0.01 1.84 6.27 1.63 to 24.11
Normal (250K-490K u/L) 44 reference reference reference reference
High (>490K u/L) 11 0.48 0.88 2.42 0.21 to 28.12
Hematocrit*Low (<33%) 66 0.03 0.84 2.23 1.11 to 4.86
Normal (33%–56%) 110 reference reference reference reference
High (>56%) 6 perfect predictor of no hemangiosarcoma
Hemoperitoneum*No 91 reference reference reference reference
Yes 91 0.01 1.05 2.85 1.28 to 6.37
*significant P-value at P<0.05.
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in only 32.4% of the dogs. Malignant splenic lesions were identified in only 42.3% of the dogs,
while the majority of splenic lesions, 57.7%, were benign. These results confirmed our hypoth-
eses. The low frequency of malignant splenic lesions and HSA found in the current study, were
similar to another study’s recent findings that only 27% of the dogs that underwent splenec-
tomy surgery due to a splenic tumor, were malignant [15].
Guidelines regarding prognosis and likelihood of splenic malignancy are needed when
making decisions with clients in private practice. The double two-thirds rule is an easily under-
standable and helpful tool that was established to better guide veterinarians and owners in
making decisions when splenic lesions were diagnosed. This rule was established based on
splenic histopathology from dogs with splenomegaly that underwent splenectomy surgery or
necropsy at a veterinary teaching hospital [13]. The fifty-fifty rule is also sometimes used dur-
ing clinical decision making, and this rule was based on a study that identified neoplastic
lesions in 50% of the canine spleens submitted to a diagnostic laboratory, and approximately
50% of the neoplastic lesions were diagnosed as HSA [20]. Since these seminal studies, preop-
erative diagnostic tools have advanced, potentially leading to increased detection of splenic
masses and nodules with and without concurrent splenomegaly. Breeds, longevity, and client
expectations have also been changing [21,22]. Recent studies have therefore been reevaluating
likelihood of splenic malignancy and HSA based on different subsets of criteria, and other fac-
tors are being considered in guidelines to assist in clinical decision-making
[7,8,11,15,19,23,24]. Our study differed from other studies in that we included dogs that had
both primary and incidental splenic masses with and without hemoperitoneum, and splenec-
tomies were performed at a privately-owned specialty clinic.
This study identified four predictors (decreased PLT, decreased HCT, smaller diameter of
largest splenic lesion, and presence of hemoperitoneum) of increased likelihood of an HSA
diagnosis, and three of these (presence of hemoperitoneum, decreased HCT, and smaller
diameter of largest splenic lesion) were also predictors for splenic malignancy including HSA.
These risk factors were also similarly identified in multiple other studies [4,10,12,19,23,25,26].
Currently, preoperative diagnostics do not provide conclusive evidence regarding malig-
nancy of splenic masses in dogs. Cytopathology is sometimes used to evaluate splenic masses
prior to surgery; however, this diagnostic is not always useful nor recommended. Risks include
Table 6. Summary of multivariable analysis and splenic malignancy including hemangiosarcoma.
Categorical variable Level Number P-value Coefficient Odds ratio (OR) OR 95% Confidence Interval
Hematocrit*Low (<33%) 66 0.004 1.28 3.59 1.51 to 8.54
Normal (33%–56%) 110 reference reference reference reference
High (>56%) 6 perfect predictor of no malignancy
Diameter of largest nodule*centimeters 143 0.002 -0.11 0.9 0.84 to 0.96
Hemoperitoneum*No 91 reference reference reference reference
Yes 91 0.02 1.04 2.82 1.15 to 6.88
Platelet group Very low (0-59K u/L) 30 0.69 -0.27 0.76 0.20 to 2.92
Low (60K-117K u/L) 38 0.04 1.35 3.87 1.08 to 13.86
Low normal (118K–249K u/L) 57 0.99 0.01 1.01 0.32 to 3.15
Normal (250K-490K u/L) 44 reference reference reference reference
High (>490K u/L) 11 0.11 1.88 6.53 0.65 to 65.51
Primary surgery No 33 reference reference reference reference
Yes 149 0.06 2.04 7.66 0.94 to 62.48
*significant P-value at P<0.05.
https://doi.org/10.1371/journal.pone.0314737.t006
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the potential for iatrogenic mass rupture that may lead to abdominal hemorrhage and the
seeding of tumor cells into the body wall. Additionally, the low exfoliating potential of HSA,
hemangioma, and hematoma masses further complicates cytopathologic evaluation [13,27]
and cytology results do not necessarily correlate with histopathologic findings for splenic mas-
ses; one study found that cytology correlated with histopathology only 61% of the time [28].
Another recent study found that cytology of canine splenic lesions had a high specificity of
95.5% but a low sensitivity of 64.3% and negative predictive value of 51.2%, indicating that
cytology might incorrectly diagnose nearly half of malignant lesions as benign [29].
Hematologic abnormalities have been documented in dogs with HSA and splenic malig-
nancies [8,12,25,30,31]. Specifically, thrombocytopenia and anemia have been found to be
associated with a higher risk of perioperative death or shorter postoperative survival times in
dogs undergoing splenectomies [19,32]. An early study [14] found that thrombocytopenia was
the most common abnormality occurring in 75% of the dogs with HSA, and dogs with HSA
had significantly lower PLT compared to dogs with other types of splenic masses; in addition,
25% of the dogs died due to hemostatic abnormalities [14]. Our study supported previous find-
ings, as dogs with low PLT (60K-117K u/L) were 21.4 times more likely to have HSA when
compared to dogs with normal PLT; furthermore, only four dogs with HSA in our study had
normal or high platelet counts. Our study also found that dogs with low HCT (<33%) had 3.1
times the odds of an HSA diagnosis compared with dogs with a normal HCT. Previous studies
[8,30] also have found that dogs diagnosed with HSA had significantly lower PCV and that
PCV was higher in dogs with benign splenic masses [8]. Similarly, no dogs with HSA in our
study had a high HCT. It is possible that some of our findings may be attributed to the pre-
sumption that malignant splenic masses might be more likely to rupture and cause intermit-
tent or continuous hemorrhage causing anemia and thrombocytopenia.
In our study, there were 33 dogs that underwent a splenectomy when a splenic lesion was
identified incidentally. Of the 33 incidental splenic lesions, 31 (93.9%) were benign. The find-
ings from a recent study [7] that used records from both a university and specialty clinic
aligned with the less common fifty-fifty rule [20]. That study [7], however, only evaluated dogs
that presented with hemoperitoneum and/or clinical signs indicative of splenic disease; there-
fore, dogs that had splenic masses identified incidentally were likely not included in their
study, and this might have led to the exclusion of additional benign splenic diagnoses. Further-
more, a recent study [8] evaluated only incidentally identified splenic masses in dogs without
concurrent hemoperitoneum, and they found that 70.5% of these were benign. Considering
the large majority of incidentally detected splenic masses diagnosed as benign lesions, pru-
dence is warranted when performing splenectomies in these cases, as splenectomy itself can
result in adverse events.
Other tests, algorithms, and risk factors have been explored to better assess risk of malig-
nancy and HSA in splenic lesions [12,26,33,34]. Hemoperitoneum is often cited as one of the
predictive factors, and incidence of malignancy for dogs with hemoperitoneum has been
reported generally between 60%–80% [23,26,33,35], with the majority of the malignancies
attributed to HSA. Our study also identified hemoperitoneum as one of the significant predic-
tors of malignancy and HSA, as 60.4% of the 91 dogs with hemoperitoneum had a splenic
malignancy including HSA. Another study evaluated specifically anemic dogs that received
transfusions during treatment for hemoperitoneum or a splenic mass, and malignancy was
identified in 76.1% of the dogs and 70.4% having HSA [12]. A recent meta-analysis confirmed
those findings that over 70% of dogs with nontraumatic hemoperitoneum due to a splenic
mass, had a malignant splenic lesion [24].
Splenic mass relative size and number of nodules have also been considered as predictors of
malignancy and HSA. Our study did not find an association between number of nodules and
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risk of malignancy or HSA, and this lack of association was also found in another study that
evaluated solitary versus multiple splenic lesions in dogs [33]. Our study found that size of the
largest splenic lesion was associated with risk of HSA. As the largest splenic nodule increased
in diameter, the dog’s risk of having an HSA diagnosis decreased; larger lesions were more
likely to be benign. This corroborates other studies’ findings [10,17]. One study found that
masses larger than 7 cm were more likely to be benign [17], and another found that benign
splenic masses had significantly larger mass-to-spleen size ratios and increased splenic weight
as a percentage of body weight as compared to malignant tumors [10]. These findings might
be attributed to the potentially faster growth rate of smaller masses, which might initiate rup-
ture more readily [17]. Malignant masses are also more likely to have disorganized architecture
that predispose them to spontaneous rupture sooner compared to benign lesions [11]. Other
studies, however, have not found an association between splenic mass size and histopathologic
diagnosis or overall prognosis [13,20].
Historically, German shepherds (GSD), Retrievers, and Boxers were overrepresented in
cases with hemangiosarcoma [1,4,13]. Recent studies have found associations with breed and
weight or size of dog and likelihood of HSA or splenic malignancy [7,11,31]. One study found
that smaller dogs were less likely to be diagnosed with HSA, but they did not find a significant
difference in occurrence of splenic malignancy when comparing small versus large dogs; how-
ever their cutoff for small versus large dogs was 27.8 kg thereby including considerably large-
sized dogs in their small category [31]. Other studies have found differences based on size and
breed with large-breed dogs being more likely diagnosed with HSA and splenic malignancy or
hemorrhage [7,11,36]. All 6 of the GSD in our study were diagnosed with HSA; however, the
overall breed-size category was not a statistically significant predictor of HSA in our study.
This could be due to small numbers of dogs in each breed such that most of the dogs (133/182,
73.1%) in our study were either mixed-breed or represented by a breed that had 5 or less dogs,
thus those 133 dogs were assigned to the breed-size category based on size. This might also
suggest that breeds differed in our study as compared to other studies due to geographic loca-
tion or clinic type, or that breed demographics are changing and were represented by a large
proportion of mixed breeds in our study. However, the breeds assigned in our study were
based on owner-report without genetic analysis or breed documentation. This could have
resulted in misrepresentation and inaccurate categorization of breeds. Furthermore, there
were breed bans in one of the counties adjacent to the clinic in our study. The dogs that might
have been phenotypically characterized as belonging to one of the banned breeds, might have
instead been assigned a breed, as per owner report, that was not banned. These suppositions
should not be undervalued and may be noteworthy considering other reports of breed predis-
position to HSA or splenic malignancy.
The survival to discharge rate in this study was 91%. Of the 16 dogs that were not success-
fully discharged, 50% had a malignancy diagnosis, and 50% had benign disease. Dogs undergo-
ing splenectomy have been shown to have hemorrhage-associated hemostatic dysfunction and
post-operative thrombosis including portal system thrombosis and pulmonary thromboembo-
lism [19]. Although some previous studies showed a low mortality rate in dogs with splenec-
tomy due to splenic hematomas [18], a recent study found that dogs that underwent
splenectomy due to benign splenic masses and hemoperitoneum, died prematurely at a high
and clinically significant rate [17]. Considering the potential for adverse outcomes and compli-
cations leading to shortened survival times, further caution and an exhaustive exploration of
risk factors for malignancy might be warranted when splenectomy decisions are made in dogs
with splenic lesions or hemoperitoneum.
There were several limitations with our study. It was retrospective and relied on data col-
lected from review of medical records. Some of the information was also therefore sometimes
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Canine splenectomy, splenic malignancy, and hemangiosarcoma at a surgicalspecialty clinic
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based on owner report such as breed and age of dog. Because of the retrospective nature and
the sole inclusion of dogs that underwent splenectomy, dogs that were presented to the clinic
for splenic masses or spleen-related clinical signs but did not undergo surgery, were not
included. Such dogs could have been euthanized, died prior to or during surgery, or clients
could have elected at-home medical management or palliative care. Inclusion of these groups
could have resulted in different findings. Furthermore, if clients did not consent to sample sub-
mission and histopathology, particularly if their dog had died or been euthanized during sur-
gery, those dogs could not be included in our study. The lack of inclusion of those dogs could
have resulted in fewer malignant disease processes diagnosed. Future studies might consider
prospectively evaluating splenic and other organ pathology of those dogs while removing the
financial burden associated with histopathology submission. For those dogs that elected medi-
cal management and at-home care in lieu of surgery, future studies might consider following
those dogs, outcome, survival, and histopathology post-mortem. Another limitation was that
histopathology slides were read by multiple pathologists, and the slides were not available to be
reviewed by the authors. Biopsies and histopathologic evaluation of the liver of the dogs were
also not included; liver biopsies could have provided further information regarding malig-
nancy [37]. Our study also did not include long-term follow-up of the dogs, thus overall out-
come could not be assessed.
Conclusions
Our study found that the majority of dogs that underwent splenectomy surgery had benign
splenic lesions. Based on our findings that hemoperitoneum, anemia, thrombocytopenia, and
smaller diameter of splenic lesions were risk factors for HSA especially, and the first three can
be associated with hemorrhage, it is suggested that these associations be strongly considered
when evaluating splenic masses and deciding to perform splenectomies. Furthermore, consid-
ering that the large majority (93.9%) of incidentally found splenic masses were benign, extra
caution is warranted if splenectomy is being considered in a dog without clinical signs indica-
tive of malignant splenic disease or clear risk factors for malignancy.
Overall prevalence of splenic malignancy including HSA may be overestimated in some
canine populations if clinicians are evaluating non-ruptured splenic masses in dogs being seen
in private practice. The information provided by our study may be useful for veterinarians
when evaluating options, risk factors, and prognoses for HSA and the possibility of malignancy
and when discussing the above with clients. Canine demographics, breed distributions, and
longevity are continually changing, thus clinical patterns and diagnoses likely also continually
change and differ from patterns established decades prior.
Author Contributions
Conceptualization: Brigita Ziogaite.
Data curation: Brigita Ziogaite, Elena T. Contreras.
Formal analysis: Elena T. Contreras.
Investigation: Brigita Ziogaite.
Methodology: Brigita Ziogaite, Elena T. Contreras.
Project administration: Brigita Ziogaite.
Resources: Jason E. Horgan.
Supervision: Brigita Ziogaite.
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Canine splenectomy, splenic malignancy, and hemangiosarcoma at a surgicalspecialty clinic
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Validation: Jason E. Horgan.
Visualization: Elena T. Contreras.
Writing – original draft: Brigita Ziogaite, Elena T. Contreras.
Writing – review & editing: Brigita Ziogaite, Elena T. Contreras, Jason E. Horgan.
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